Radio navigation system



MY 20, 1948. G. MoUNTJoY ET Ax. 2,445,361

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RADI() NAVIGATION SYSTEM Delaware Application April 20, 1945, Serial No.589,320

20 Claims.

i Our invention relates to radio navigation systems and particularly tosystems of the type utilizing the time diierence in the propagation ofradio pulses from synchronized ground stations.

Navigation systems of this type employ pairs of synchronized groundstations that transmit radio pulses having at the instant of radiation afixed time relation to each other. Each Pair of ground stationspreferably transmits pulses at its individual assigned repetition ratefor the purpose of station selection. The pulses are radiated toreceiving equipment located on the aircraft or ship whose position is tobe determined. By means of the receiving equipment, the operator on thecraft determines the time difference between the pulses from the twotransmitter stations of one pair as they arrive at the receiver. Sincethe radio pulses travel from the ground transmitters to the receiver ata known propagation rate (i. e., at the velocity of iight), it is knownthat the position of the craft is at some point on a line correspondingto the time diierence reading. By obtaining the time difference readingfrom a second pair of ground stations, a second line corresponding tothe second time difference reading is obtained, and the intersect pointof the two lines is the position of the craft. Special maps having timedifference lines printed thereon for the several pairs of groundstations are provided for use with the navigation system.

In order to measure the time difference in the arrival of successivepulses from a pair of ground stations, timing marker pulses that have aknown time interval between them are generated. Also, pulses having adefinite time relation to the time marker pulses are generated for thepurpose of driving or synchronizing cathode-ray deilecting circuits.These deilecting circuits produce cathode-ray sweep traces on which themarker pulses and/or the received ground station pulses appear.

For the purpose of selecting a particular pair of ground stations, theoperator selects a par ticular pulse repetition rate for the driving orsynchronizing pulses corresponding to the repetition period of thepulses transmitted from said pair whereby the deecting circuits may besynchronized with the received pulses from the selected. pair of groundstations. Thus a particular pair of ground stations is selected at thereceiver apparatus by turning a station selection switch to the positionindicated on the receiver panel for obtaining sweep synchronizing pulseshaving the same repetition period as that of the pulses beingtransmitted from the selected pair of ground stations. Now the receivedpulses from the selected pair of ground stations can be made to appearstationary on the cathode-ray sweep or trace whereas those received fromthe other pairs of ground stations will move rapidly along the sametrace.

In operation, the pulses from the two transmitter stations of a selectedpair of `stations (which pulses will be referred to as A and B pulses,respectively) are made to appear on two cathode-ray traces,respectively. The B pulse is identified as the pulse that occurs afteror follows the mid-point of the other pulse period, or. in some systems,may be otherwise identified. The

, A and B pulses are brought into alignment or coincidence by moving theA pulse along its cathode-ray sweep trace, this being done by adjustingthe starting time of the cathode-ray sweep. It is then possible tomeasure the time displacement of the sweep required for pulse alignment.This may be done, for example, by blanking out the portion of theadjustable trace from the center of the deecting wave cycle and bycounting 1000 ps. timing markers appearing on the remaining portion ofthe trace. Thus, the desired time difference between pulses isdetermined to a fractional 1000 ps. period. A precise determination ofthe fractional 1000 as. period is made possible by employing a secondcathode-ray sweep that is fast and which occurs at the start of theunblanked portion of the slow-sweep trace and lasts for the saidfractional period whereby 10 ps. and as. timing marks occurring duringthe fractional period appear on an expanded trace.

An object of the present invention is to provide an improved method ofand means for determining the time diiierence between electrical pulses.

A further object of the invention is to provide improved receivingequipment for a radio navigation system of the type utilizing thepropagation of radio pulses from pairs of synchronized ground stations.

A still further object of the invention is to provide an improved methodof and means for indicating the time difference between radio pulsestransmitted from synchronized ground stations.

A still further object of the invention is to provide an improved methodof and means for obtaining a simple time marker presentation in a radionavigation system of the above-mentioned type.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which -EarlSchoenfeld and entitled Figure 1 is a block and circuit diagram ofnavigation receiving apparatus designed in accordance with oneembodiment of the invention.

Figure 1a is a block and circuit diagram of the pulse generating unitshown in Fig. 1,

Figure 1b is a circuit diagram of the horizontal deiiecting fast-sweepcircuit employed in the system of Fig. 1,

Figure 1c is a block diagram representing one pair of ground radiotransmitter stations of the navigation system which transmit A and Bpulses, respectively,

Figures 2, 3 and 4 are views of the slow-sweep cathode-ray tracesappearing on the screen end of the cathode-ray indicator tube that isincluded in the apparatus of Fig. 1 and of the received pulses A and Bas they appear on the two traces, respectively, during successive stepsin aligning the pulses A and B,

Figures 5 and 6 are views of the fast-sweep cathode-ray traces on thecathode-ray tube indicator and of the received pulses A and B as ltheyappear on the two fast-sweep traces, respectively, during the nextsuccessive steps in obtaining more exact alignment of the A and Bpulses,

Figure '1 is a view showing the fast-sweep traces of Fig. 6 superimposedor collapsed for the final alignment step and showing the A and B pulsesexactly aligned and superimposed.

Figure 8 is a view of the two slow-sweep traces on the cathode-ray tubeindicator screen with a portion of the upper trace blanked out and withthe 1000 as. timing marks on the traces for obtaining the time readingin 1000 as. intervals,

Figure 9 is a View of the two fast-sweep traces on the cathode-rayindicator tube screen with 1000 as., 100 as, and 10 as. timing marks onthe upper trace and with a 50 as. cross-hair mark on the lower trace forobtaining the time reading of the fractional 1000 as. intervals,

Figure 10 is a group of graphs that are referred to in explaining theoperation of the system shown in Fig. 1, and

Figure l1 is a view showing the relation of the cathode-ray trace withrespect to the horizontal defiecting waves and also with respect to thetiming marker pulses.

In the several figures, similar parts are indicated by similar referencecharacters.

The pulse generator and station selection circuit which will now bedescribed under the headings "I'he pulse generator unit and "Countsubtraction for station selection" is the same as that described andclaimed in application Serial No. 552,146, filed August 31, 1944, in thename of Timing marker and station selection apparatus.

THE PULSE GENERATOR UNIT In Fig. 1, the pulse generating circuit forproducing the timing marker pulses and for producing the controlling orsynchronizing pulses that control the cathode-ray deflection is shown inblock diagram at the top of the ligure. It is shown in detail in Fig.1a. Referring to Figs. 1 and 1a, the pulse generator comprises a crystaloscillator III that produces a sine wave voltage of stable frequencywhich in the example illustrated is 100 kilocycles per second, therepetition period being 10 microseconds. The frequency of the crystaloscillator output may be increased or decreased slightly by a manualadjustment asindicated at the control knob II for obtaining a "ne rightor left drift of a received Pulse 9.11 a

vention is cathode-ray sweep trace, the rate of drift being slow enoughto be useful on fast-sweep presentation.

The crystal oscillator I0 drives a blocking oscillator I2 or the like toproduce periodic pulses which, in the present example, also recur at therate of k. c. per second. 'I'he repetition period or time intervalbetween successive pulses is, therefore, 10 microseconds.

'I'he frequency of the 10 as. pulses is divided by five by means of asuitable frequency divider I5 such as a second blocking oscillator toproduce 50 us. pulses. While specific values are being given for theseveral frequency division steps, the innot limited to these particularvalues.

The 50 as. pulses are applied through a lead I4 to a frequency dividerI6 of the counter type described in White Patent 2,113,011. It dividesthe frequency by two to produce 100 as. pulses. Also, an additionalcircuit is provided so that the divider I6 may be made to lose a countfor the purpose of obtaining a dlierent selected pulse repetitionperiod.

The divider I6 comprises a counter circuit portion including an input or"bucket capacitor I1, a pair of diodes I8 and I9, a storage capacitor 2|and a blocking oscillator portion 22. In addition, it includes a pair ofdiodes 23 and 24 associated with the storage capacitor 2l for thepurpose of making the divider I6 lose a count upon the application of a.pulse from a conductor 26 as will be explained hereinafter. 'I'heblocking oscillator 22 comprises a vacuum tube 21 and a transformer 28coupling the plate circuit to the grid circuit. The cathode circuitincludes a biasing resistor 29, bypassed by a capacitor 3I, andconnected in series with a bleeder resistor 29. A transformer 32supplies the 100 as. pulses from the divider I6 to a frequency divider33 which also is of the type which may be made to lose a count.

The frequency divider I 6 operates as follows: Each of the 50 as. pulsesof positive polarity from the lead I4 puts a predetermined charge on thecomparatively large capacity storage capacitor 2| as a result of a pulseof current through the comparatively small bucket capacitor I1 andthrough the diode i 9, the capacity of the capacitor I1 being smallenough so that capacitor I1 receives full charge before the terminationof an applied pulse. At the end of this current pulse, the capacitor I1is discharged to ground potential through the diode I8. 'I'he next 50as. pulse puts an additional current pulse into capacitor 2 i, thisraising the voltage across capacitor 2i sufiiciently to trigger theblocking oscillator 22 whereby a pulse is produced across thetransformer 28 as is well understood in the art. The pulse thus producedis applied to the divider 33 with positive polarity. At the same timethe blocking oscillator 22 discharges the capacitor 2i to bring it backto ground potential.

The frequency divider 33 divides the frequency by ve to produce 500 as,pulses. It includes a counter portion comprising a bucket capacitor 36,a pair of diodes 31 and 38, and a storage capacitor 39. It also includesa blocking oscillator portion 4I comprising a vacuum tube 42, a feedbacktranformer 43, a biasing resistor 44' and a bypass capacitor 46.

As in the preceding divider vided in the divider 33 a pair of diodes 41and 48 for subtracting counts. In the divider 33, however. theapplication of a pulse from a conductor I 6, there is pro- 69 willsubtract one. two or three counts depending upon the position of thestation selection switch.

The 500 ps. pulses are supplied over a conductor 6| to a frequencydivider 52 that divides by two to produce 1000 as, pulses. The divider52 is similar to the divider IB with the count subtracting diodesomitted. i

The 1000 ps. pulses are supplied to a frequency divider 60 that dividesby ve to produce 5000 ns. pulses which, in turn, are supplied to afrequency divider 59 that divides by four to produce 20,000 ys. pulses.The the divider B2 except for constants.

The 20,000 as. pulses may be passed through a clipping circuit 60 andsupplied over a. conductor 6| to a square wave generator 65 (Fig. 1)such as on Eccles-Jordan oscillator, for obtaining a square thedifference in circuit Vwave having a repetition period of 40,000 as Fromthis square wave are obtained, by means of suitable wave shaping anddelay circuits described hereinafter, the desired driving orsynchronizing pulses for the horizontal deflection.

Y The 20,000 ps. pulses are also supplied over a conductor 62 andthrough a bucket capacitor 63 of the first count subtraction circuit toa station selection switch 60; they are also supplied to the secondcount subtraction circuit through a coupling or blocking capacitor 66 oflarge capacity to a second station selection switch 61 which is gangedwith the switch El! as indicated by the broken line 63, the two switchesbeing operated by a knob 05'.

At the switch 6d, alternate switch contact points are connected to thefeedback conductor 26 whereby at these switch point positions the 20,000us. pulses are fed back to the divider |6 to subtract counts. It may bedesirable because of distributed or stray leakage in the switch 66oreapacitcrs B3 to connect the switch arm 64 to ground through a lmegohm resistor 55 to permit charges to leak of.

At the switch 61, the last six switch contact points are connected inpairs, the three pairs of contact points 4t2-#3, #r4-#5 and #f3- #7being connected through bucket capacitors 1|, 12 and 13, respectively,to the feedback conductor i9 which leads to the second count subtractioncircuit. Thus, with sw-itch 6l in any one of the last six positions,20,000 as. pulses are applied to the divider 33 to subtract counts.

Before discussing in detail the operation of the count subtractingcircuits for station selection, it may be noted that the desired timingmarker pulses are obtained at various points along the frequency dividercircuit. In the present system, the 10 ps. lpulses are supplied from theblocking oscillator l2 through a delay network I3 to an output lead 3|.50 its. pulses of opposite polarities are supplied to leads |92 and |98.The 100 as., 500 as. and 1000 as. pulses are supplied to a common outputlead |96. 1000 its. pulses of opposite polarity are supplied to anoutput lead 2H. The marker pulses are applied through circuitshereinafter described to the vertical defiect'ing plates of acathode-ray tube |29. The cathode ray of the tube |29 is deflectedhorizontally by either a slow-sweep or a iast-sweep deiiecting wave thatis in synchronism with the 40,000 ps. square wave from the Eccles-Jordanoscillator 65 (Fig. 1). It is evident that the 40,000 its. horizontaldeection cycle has a fixed time relation to the timing marker pulses.

dividers 56 and 59 are similar toV COUNT sUBTn-Ac'rron ron STATIONSELECTION 'Referring now `more particularly to the feature ofsubtracting counts for the purpose of station selection, specic puiserepetition rates for a plurality of pairs of ground transmitter stationswill be referred to by way of example to aid in explaining theoperation.

It will be assumed that the iirst pair of ground stations transmit the Apulses with a repetition period of 40,000 as. and transmit the B pulseswith a like repetition period; that the second pair of ground stationstransmit A and B pulses having a repetition period of 39,900 Ils.; thatthe third pair transmits 39,800 as. pulses; that the fourth pair'transmits 39,700 ps. pulses, etc. It is apparent that for stationselection at the receiving apparatus. the operator mus-t be able toselect corresponding repetition periods for the output of the squarewave lgenerator 65 which controls the cathode ray Vdeflection cycle;namely, periods of 40,000 its.; 39,900 as.; 39,800 as.; 39,700 es.;39,600 as.; etc.

It will be noted that several repetition periods differ from each otherby as. or by integral multiples thereof. and that this corresponds torepetition period differences of 50 as. or integral multiples thereof atthe output of the frequency divider chain. i. e., at the input of theclipper 60. Therefore, the desired repetition period can be obtained byshortening the 20,000 as. period by 50 by 100 ps., by 150 as., etc.

For example, to obtain the 39,900 its. repetition period, the switches66 and 61 are moved to the No. 1 switch contact points. At this switchposition the 20,000 as. pulses from the lead 52 are fed back by way ofthe bucket capacitor 63. the switch 6d and the conductor 26 to thefrequency divider I6 only. Upon the occurrence of a 20,000 ps. pulse, itproduces a pulse of current through the bucket capacitor 63 and throughthe diode 23 to add a charge to the storage capacitor 2|. At the end ofthe pulse, the capacitor B3 discharges through the diode 2t to itsoriginal potential. By properly selecting the capacity value of thebucket capacitor 63, the added charge is made equal to the charge whichis added to the capacitor 2| by a single 50 as. pulse. Thus, the 20,000as. pulse causes the blocking oscillator 22 to fire one lpulse earlieror 50 as. sooner than it normally would whereby the desired repetitionperiod of 19,950 as. at the clipper 60 or 39,900 as. at output of theE.J. oscillator B5 is obtained. It may be noted that, in the examplegiven, each time a 20,000 as. pulse occurs, the divider IE divides byone instead of by two.

To obtain the 39,800 ps. repetition period, the switches 64 and 61 aremoved to Position #2. Now the 20,000 ps. pulses are applied through thebucket capacitor 1I to the divider 33 and upon the occurrence of a20,000 as. pulse. It applies a charge to the capacitor 39 through thediode B8. At the end of the .pulse the capacitor 1I discharges throughthe diode 41 to its original potential. The capacitor 1| is"given acapacity value such that this charge applied by the 20,000 as. pulse isequal to the charge applied by a, single 100 ps. pulse. Thus, upon theoccurrence of a 20,000 as. pulse, the blocking oscillator 4| res onepulse early or 100 as. sooner than it normally woulc whereby the desiredrepetition period of 19,90( its. is obtained at the clipper 60 and arepetitior period of 39,800 ps. is obtained at the output o` the E.J.oscillator 55. It may be noted that il the example given, the divider 33divides by fou` instead of by iive upon the occurrence of each 20,000us. pulse.

oscillators 22 At the switch position, the divider I6 again triggers 50its. early and the divider 33 triggers 200 as. early or a total of 250us. for the two dividers. Thus, the repetition period is 19,750 lis, atthe input to clipper 60 or 39,500 lis. at the output of the E.J.oscillator 65.

At the #16 switch position, only the divider 33 receives the 20,000 ps.pulses. These pulses are applied through the capacitor 13 which isadoscillator output.

At the #7 switch position, both of the dividers I6 and 33 lose counts,divider I6 triggering 50 ps. early and divider 33 triggering 300 iis.early, or a total of 350 repetition period is E.J. oscillator output.

It may be preferred to employ a different group of repetition periodsthan the group of 40,000 ps., 39,900 us., etc. assumed above. By maln'ngthe of repetition periods of 50,000 In order to obtainl a more ps.,49,900 Irs., etc.

rapid right drift" CATHODE-RAY TRACE AND TIMING R PRESENTATIONslow-sweep wave K and of the second fast-sweep wave It-i may be adjustedby adjusting a multivibrator I0! by a knob |02' (Fig. 1), and byadjusting a une point d of the deiiecting wave cycle ing wave L and the1000 frs. timing markers are A and B pulses. The time interval has notyet been determined fractional 1000 as. interval can be estimated onlyroughly on the slow-sweep scale.

this lower trace 50 us, marker pulses are made to appear. The second ofthese 50 its. marks (counting left to right) is used as a cross-hairmarker.

The fractional 1000 ps. interval is found by counting the 100 lis. and10 ps. marks on the upper trace and by estimating the number ofmicrosecond units lying between the last counted 10 as. marker on theupper fast trace and the 50 as. cross-hair marker on the lower fasttrace as explained more fully hereinafter.

Before describing the method of operation in more detail. the receiversystem as illustrated in Fig. 1 will be further described.

DESCRIPTION F CATHODE-RAY TRACE PRODUCING CIRCUITS, MIXING CIR- CUITS,ETC. OF FIG. 1

Referring to Fig. l and to the graphs of Figs. i and 11, theEccles-Jordan oscillator 5S is triggered by the 20,000 as. pulsessupplied over the conductor 6| to produce a rectangular voltage wave C.Timing pulses from the counters of the pulse generator unit are shown atthe tops of the Figures 10 and 11.

The front or rising edges of the wave C trigger this multivibrator |0|to produce a rectangular wave similar to the wave F, the back edge ofthe narrow pulse portion of this wave being adjustable by means of theknob |02'. ,This timing of the back edge controls the starting time t ofthe second sweep portion c-d of the slow-sweep de` flecting wave K aswill soon be apparent. The multivibrator |0| may be any one of theseveral well known types such as, for example, the one described inBritish Patent 456,840 to White and in the A. I. E. E., vol. 60, 1941,pp. 371 to 376. To obtain a tighter lock-in of the multivibrator |0|with respect to the timing marker pulses, 500 as. lock-in pulses fromthe counter 33 are supplied over a lead |00 to the multivibrator |0i.

In order to obtain a more precise timing adjustment than can be made atthe multivibrator |0|, the wave F that is shown in Fig. 10 is obtainedin Fig. 1 from an adjustable delay circuit |06 that integrates and clipsthe narrow pulse portion of the rectangular wave from the multivibrator|0| in a manner well known in the art to provide a fine timingadjustment of the back edge of the wave F. The fine timing adjustment ismade by operating a knob |06 that, for example, changes the capacity ofthe integrating circuit. If preferred, the iine timing adjustment of theback edge of the wave F may be obtained by a second multivibrator thatis substituted for the integrating-clipping circuit |06. Such amultivibrator would be similar to the multivibrator |0| but designed toprovide a small timing change.

The rectangular wave C from the multivibrator |0| is also passed througha. differentiating circuit |0`| to produce the differentiated wave Ewhich, after clipping in a mixer circuit H0, appears as the first andthird pulses of the wave H in the illustration of Fig. 10. Likewise, thewave F from the delay circuit |06 is passed through a differentiatingcircuit |03 to produce the dilerentiated wave G which, after clipping inthe mixer l0, appears as the second and fourth pulses of the wave H inthe illustration of Fig. 10. The mixer circuit H0, as indicated above,functions both to clip oi the negative pulses of `waves E and G and tomix the remaining clipped positive pulses. Thus, the wave H is obtainedat the mixer output, the mixer, which may consist of two vacuum tubeshaving a common anode resistor, having reversed the polarity of thepulses. It will be seen that the front edges of alternate 0 pulses ofthe wave H coincide with the back edges of the wave F.

The wave H is supplied over a conductor ||2 to the fast-sweep deflectingcircuit and a slow-sweep circuit ||5 comprising, respectively, a vacuumtube IIB and a network ||1, and a. vacuum tube ||8 and a network H9. Thetubes H6 and are coupled anode-to-grid through a capacitor |2| and agrid-leak resistor |22. The narrow negative pulses of wave H produce thefast-sweep waves f--g and h-i (in solid line in Fig. 10) of wave Ihaving the same duration as the pulses of wave H. The slow-sweep wavesa--b and c-d of wave K are initiated by the positive pulses of a wave J(Fig. 10) that is obtained by differentiating the wave H (reversed inpolarity by the tube IIB) by means of the coupling capacitor |2| and thegrid-leak resistor |22. The deecting waves I and K are applied from thecircuits and I5 through a wave selecting switch |23 and through apush-pull amplifier |24 and coupling capacitors |26 and |21 to thehorizontal deecting plates |23 of the cathode-ray indicator tube |29.

The switch |23 has iive contact points and ve corresponding switchpositions, referred to as operating positions, which are identied,reading clockwise, as positions #1, #2, #3, #4 and #5. There are sixother operation positions switches, described hereinafter, that likewisehave these five switch positions and which are ganged with the switch|23.

Switch |23, when in operation positions #1 and #4, functions to applythe slow-sweep wave K to the horizontal deecting plates |28 and, when inoperation positions #2, #3 and #5, functions to apply the fast-sweepwave I to the detiecting plates |23.

Tm; FAST-Sweep CIRCUIT Referring more specifically to the defiectingcircuit for producing the fast-sweep wave I, as shown in Fig. 1b thenetwork of deilecting circuit comprises two sections consisting ofcathode resistors |3| and |32 shunted by capacitors |33 and |34,respectively, identiiied as network sections ||1a and ||1b. The networkIllV further comprises a delay line section ||1c comprising seriesresistor |36 and shunt capacitors |31 connected across the cathoderesistor |3| and terminated in a resistor |38 and in the cathoderesistor |32. The fast-sweep wave I is taken oi the resistor |33 throughan adjustable tap |39, the setting of which determines the amplitude orvoltage level ei (Fig. 11) of the wave I.

In operation, the capacitors of the network sections ||1a and I|1b arecharged through the anode resistor |4| and the tube ||6 to a certainvoltage level between successive pulses of the wave H to bring the tap|30 to the voltage el. Upon the occurrence of each negative pulse of thewave H, the tube I6 is driven to cut-olf and the capacitors |33 and |34discharge through the resistors |3| and |32, respectively. The sectionIlla comprising capacitor |33 and resistor |3| has a fast time constantwhereby the discharge of capacitor |33 produces a voltage of steep slopeacross resistor |3l. The section Illb comprising capacitor |33 andresistor |32 has a slower time constant whereby the discharge ofcapacitor |34 produces a voltage of less slope across resistor |32.These two voltages of diierent slopes appear at the tap |39 as the sumof the two voltages with the voltage of the steeper slope slightlydedeilecting circuit I layed by the delay network section ||1c. Onereason for providing this slight delay of a few microseconds (50 as. inthe example shown) is to make the 50 as. cross-hair mark fall at a.suitable point on the expanded portion of the fast-sweep. 'Ihe wave formof the wave I following the 50 as. delay is approximately logarithmic.

It should be understood that the fast-sweep wave I need not be of thewave form described and, in fact, may be linear although some form ofincreased expansion at the left end of the fast-sweep trace must beprovided for the accuracy desired in the present embodiment of theinvention. Such expansion may be obtained by employing either alogarithmic wave shape or an exponential wave shape. for example.

'Ihe above-described fast-sweep deflecting circuit is described andclaimed in application Serial No. 583,255, led March 1'7, 1945, in thename of George D. Hulst, Jr., and entitled Cathode ray deflectioncircuit.

THE SLOW-SWEET CIRCUIT Referring more specifically to the slow-sweep I5,the network 9 consists of a cathode resistor |42 that has an adjustabletap |44 thereon and which is shunted by a capacitor |43. The operationlis as follows: Each time one of the positive short pulses of the wave Jappears on the grid of the tube ||6, the capacitor |43 is chargedsuddenly from the anode voltage supply through the tube ||6 to a certainvoltage level to bring the tap |44 to the voltage level e1 (Fig. l1). Atthe end of the positive pulse, the capacitor |43 discharges slowlythrough the resistor |4| thus producing either the slow-sweep sawtoothwave a-b or the sawtooth wave c-d at the tap |44. It will be noted thatthe duration and amplitude of each of the sawtooth components a-b andc-d of the wave K depend upon the interva1 between successive positivepulses of the Wave J. I

As previously noted. the starting time t of the second slow-sweep wavec-d is determined by the adjustment of the back-edge of the wave Fwhereby the start of the wave c-d may be made to precede the received Apulse by the same amount that the start of the wave a-b precedes thereceived B pulse, this being the condition of alignment of the A and Bpulses. It should also be noted that the wave a-b is identical with thecorresponding portion of wave c-d whereby exact alignment of the A and Bpulses on the cathode-ray traces is obtained (as shown in Fig. 4) whenthe above-described timing relation exists. The remarks of thisparagraph apply also to the fast-sweep waves f-g and h-i of the wave I,the condition of inal alignment on the fast-sweep traces (with thetraces collapsed or superimposed) being illustrated in Fig. 7.

HORIZONTAL DEFLEcTINc AMPLIFIER The push-Dull amplifier |24, throughwhich the deiiecting waves I and K are selectively applied to thehorizontal deflecting plates |28, comprises an amplifier tube |46 havinga cathode biasing resistor |41. The anode of the tube |46 is coupled tothe grid of a, phase inverter tube through a coupling capacitor |48 andthrough a, voltage divider comprising resistors |49 and |53. A capacitor|52 of 5 mmf. is connected across the series resistor |49 to compensatefor the gridcathode capacity of the tube 5|. The tube |5| is providedwith a cathode biasing resistor |54.

A bleeder resistor |56 is connected from the 12 anode of the tube |46 tothe arm of a bias control switch |51. The #l and #4 contact points ofthe bias switch |51 are connected to the cathode end of the cathoderesistor |41 whereby, when the switch arm is on either the #1 or #4contact points (the slow-sweep positions), an additional iesgative biasis applied to the grid of the tube The anodes of the amplifier tubes |46and |5| are connected through coupling capacitors |53 and |59,respectively, to the horizontal defiecting plates |28.

THE RADIO RECEIVER The A and B .pulses from a pair of ground stationsare received by a radio receiver of the superheterodyne type comprisinga :first detector and l SLOW-SWEEP TRACE SEPARATION The slow-sweeptraces a-b and C-d are separated as illustrated in Figs. 2 to 4 and inFig. 8 while the receiver is on the #1 'and #4 operation positions bymeans of a rectangular wave M (Fig. 10) supplied from the delay circuit|06 (Fig. 1) over a conductor |69 to the #1 contact point of a timingmarker and trace separation switch |1|, and over a conductor |69 andthrough a resistor |12 to the #4 contact point of said switch. When theswitch arm of the switch |1| is in either position #1 or position #4(the slow-sweep positions), the wave M is applied through a conductor|13, a, reversing tube |10 and a coupling or blocking capacitor |14 tothe upper vertical deecting plate |68. Thus, the portion of the wave M,which is negative as it appears on the upper plate |68, holds thecathode ray deflected down a certain amount during the occurrence of theslow-sweep deecting wave a-b.

FAST-Swear TRACE SEPARATION The fast-sweep traces f-g and h-i areseparated as illustrated in Figs. 5 and 6 and in Fig. 9 during the #2and #5 operation positions (fastsweep positions) by means'of arectangular wave D. This is obtained by passing a wave L (Fig. 10) fromthe E.J. oscillator 65 over a conductor |16 to adelay circuit |11. Thedelayed wave at the output of the delay circuit |11 is the wave D' (Fig.10) which is supplied to a push-pull ampliiier |8| to obtain the wave Dand the wave D of opposite polarity at the leads |82 and |83,respectively. The waves D and D', which are identica1 except forpolarity, are utilized for on and oi keying of a pair of timing markermixer tubes |18 and |19 (at upper right Fig. 1) and for operation of adierential gain control circuit (at lower left Fig. 1). These uses ofWaves D and D will be described hereinafter. The wave D is also utilizedfor cross-hair trace separation. The wave D on the lead |83 is, suppliedover the lead |83 and a conductor |84 to the #2 contact point of theswitch |1|. The wave D is also supplied from the lead |83 to the #5contact point of the switch |1| by way of a conductor |86 and apotentiometer resistor |81 having a variable tap |88 thereon, andthrough a resistor |89 and a conductor |9| to the #5 contact point. Inoperation position #5, the amount of trace separation may be adjusted bymeans of the tap |88 to bring the cross-hair mark, shown in Fig. 9, inproper relation to the trace h--i on which the timing marks appear aswill be described hereinafter.

From the foregoing it will be seen that suitable trace separationvoltages are supplied to the upper deflecting plate |68 of the tube |29by way of the switch |1| and the polarity reversing tube |10 for allswitch positions except operation posion #3 where it is desired that thetwo traces be superimposed as shown in Fig. 7.

APPLICATION OF TIMING PULSES TO CATHODE-RAY TUBE As shown in Figs. 8 and9, certain timing pulses are made to appear on the traces of thecathoderay tube |29 when the ganged switches are on the #4 and #5operation positions, respectively, these two positions being the onesfor reading the full 1000 as. intervals and for reading the remainingfractional 1000 lis. interval, respectively. When the receiver is oneither the #4 or the #5 position, the received pulses A and B do notappear on the cathode ray traces because a bias source 252 then suppliesa negative voltage over a lead 249 to block the I.F. amplifler |62. Whenthe receiver is on the A and B pulse alignment positions, i. e.,positions #1, #2 and #3, the only timing marks that appear on the tracesare as. marks and 50 as. marks in the down direction (not shown on thetraces in Figs. 2 to 1) The 10 as. timing marks in the down directionare produced by 10 as. pulses applied from the delay network |3 (at topof Fig. 1) over the conductor 8| and through a reversing tube 80 and theresistor |61 to the lower vertical deflecting plate |68 where theyappear with positive polarity to produce down marks on the cathode-raytraces. The 50 as. timing marks in the down direction are produced by 50as. pulses which are also applied to the lower deflecting plate |88,these being obtained from the 50 as. counter l5. The pulses from counter|5 are supplied over a conductor |92 and through a reversing tube |90and a resistor |93 to the deilecting plate |68 where they appear withpositive polarity to produce down marks on the cathode-ray traces. Thedelay network i3 is provided so that the 10 as. pulses on the deflectingplate |88 will occur substantially with the 1000 its. pulses, the latterhaving been delayed slightly by delay occurring in the frequency dividerchain.

Reference will now be made to the circuit for feeding timing pulsesthrough the timing marker 'and trace separation switch |1| to the uppervertical defiecting plate |88.

100 as., 500 as., and 1000 as. marker pulses are applied to the grid ofthe mixer tube |18 from a conductor |90, the 100 as. and 1000 as. pulsesbeing applied with positive polarity and the 500 as. pulses beingapplied with negative polarity. The counters l0, 33 and 52 supply thesepulses to the conductor |90 by way of the conductor 81, a capacitor |96and a lead |91, respectively.

50 as. marker pulses are applied with positive polarity to the grid ofthe mixer tube` |19 from a conductor |98 carrying timing marker pulsesfrom the counter i5, the marker pulses being applied to the grid througha resistor |99 and a capacitor 20|. Also, 500 its. marker pulses ofpositive polarity (these being the second kick of a blocking oscillatorcycle) are applied to the grid of the tube |19 from a conductor |80carrying timing marker pulses from the counter 33. v

The mixer tubes |18 and |19 are blocked alternately by the waves D andD' of opposite polarities which are' supplied from the conductors |83and |82, respectively, to the grids of the tubes |18 and |19. The waveD' is applied to the tube |18 through a capacitor 202 and a resistor203, while the wave D is applied to the tube |19 through a capacitor 208and a resistor 209.

From the foregoing, it will be seen that when the receiver is on the #5position, the tube |18 passes 100 its., 500 its. and 1000 its. markerpulses to the upper deflecting plate |88 of the cathoderay tube |29during the occurrence of the fastsweep wave h--i and while the tube |19Ais blocked, and that the tube |19 passes the 500 as. marker pulses andthe 50 ps. marker pulses (one of which provides a cross-hair mark) tothe said deflecting plate during the occurrence of the fast-sweep wavef-g and while the tube |18 is blocked. All these pulses, except the 500as. pulses passed by the tube |18, appear on the upper plate |68 to makemarks that are up on the vcathode-ray traces. The 500 ps. pulses reducethe amplitude of every fth 100 as. mark thereby facilitating thecounting of the 100 ns. marks. The resulting marker presentation is thatillustrated in Fig. 9. The method of counting the timing marks will bedescribed hereinafter.

The mixer tubes |18 and |19 have a common anode resistor 201 and theirtiming pulse cutputs are supplied to the lead |9| through a couplingcapacitor 208. The tube |18 is provided with a grid leak resistor 209and a cathode biasing resistor |2| that is shunted by a capacitor 2|2.The tube |19 is provided with a grid leak resistor 2|3 and a cathoderesistor 2M that is shunted by a capacitor 2|6.

In the #4 operation position, 1000 as. pulses of negative polarity fromthe 1000 as. pulse counter 52 are applied to the #4 contact point of theswitch |1| by way of a conductor 2`|1 through a resistor 2|8 and acapacitor 2|9. These pulses appear on the upper plate |68 with positivepolarity to produce marks that are up on the cathode-ray traces.

SLOW SW1-:EP BLANKING A right-hand portion d'-d of the slow-sweep tracec-d is blanked out when the receiver is on the #4 operation position forreading the 1000 ns. intervals (Fig. 8). This reading is `obtained bycounting all the 1000 as. marks appearing on the upper trace c-d, themarks on the lower trace a-b being ignored. The trace a--b could beblanked out when taking this reading but this is not done in theembodiment illustrated. As

indicated in Figs. 10 and 11, the above-mentioned blanking of the tracec-d is done by the wave L which has the same timing as the wave C fromthe E.-J. oscillator 65, and which, therefore, has a negative half cyclestarting at the mid-point d of the 40,000 as. deflecting wave cycle.This mid-point is, of course, 20,000 as.

from the start of the deflecting wave cycle. It is apparent that if theslow-sweep trace c--d is blanked out from said 20,000 as. midpoint d tothe end d of the trace, the amount that the starting time t'of the wavec-d has been shifted to the left (i. e., advanced in time) with respectto said mid-point can be found to a fractional 1000 as. interval bycounting the 1000 as. timing marks on the remaining left-hand portionc-d' of the trace. This is done with the receiver on the #4 operationposition, the cathode-ray traces and timing marks appearing on thecathode-ray tube screen as shown in Fig. 8.

Referring now to the blanking circuit shown in Fig. l for blanking thetrace c-d as described above, the wave L is supplied from the E.J.oscillator 65 over the conductor-16 to the #4 contact point of a,blanking switch 22|. From contact point #4 the wave L is suppliedthrough a conductor 222 and a coupling capacitor 223 to the anode of adiode 224, and over a conductor 225 to the control grid 221 of thecathode-ray tube |29, Thus, the wave L drives the cathode-ray tube |29substantially to electron beam cut-olf during negative half cycle of thewave whereby only the trace portion c-d of the upper trace appears onthe iiuorescent screen as shown in Fig. 8.

Blanking at the end oi each fast sweep is provided when in the #2, #3and#5 operation position by means of the negative portions of the wave Has it appears on the anode of the tube H6, it being noted that the tube||6 reverses the polarity of the wave H applied to its grid. The wave His supplied from the anode of tube ||6 to the #2, #3 and #5 contactpoint of the switch 22| whereby, in the #2, #3 and #5 operationposition, this wave is supplied over conductors 222 and 226 to the grid221 of the cathode-ray tube.

Tmica Banu/inca CONTROL The diode 224 is provided to control thebrilliance of the timing marks and traces on the cathode-ray tube screenby preventing changes in bias on the cathode-ray tube grid 221 due tothe application of blanking pulses. A leak resistor 22B is connectedacross the diode 224 and the cathode of the diode 224 is connected to avariable tap 228 on a bias voltage source comprising a voltage dividerresistor 229.

In operation, during the periods that the blanking waves are positive atthe anode of the diode 224, the impedance of the diode 224 is very lowso that its anode is practically at the potential of the bias orbrilliance control tap 228. Thus, regardless of the form of the blankingwave and regardless of whether any blanking Wave is being applied, thevoltage on the grid 221 of the cathode-ray tube during the cathode-raysweeps is substantially the voltage on the tap 228.

HORIZONTAL CENTERING CIRCUITS Since different centering voltages shouldbe applied to the horizontal defiecting plates |28 during the slow-sweepdeflection than during the fast-sweep deflection, these plates areconnected through resistors 23| and 232 to the arms of two live-positionswitches 233 and 234, respectively. The #1 and #4 contact points of theswitches 234 and 233 are connected to variable taps on voltage dividerresistors 236 and 231, respectively,

'cycle of an applied wave.

a slow-sweep position to a fast-sweep position or vice versa.

DIFFERENTIAL GAIN CONTROL CIRCUIT A differential gain control circuitfor the I.F. amplifier |62 of the radio receiver preferably is providedas indicated in Fig. 1 for the purpose of keeping the amplitudes of theA and B pulses substantially alike at the receiver output, thusfacilitating the A and B pulse alignment. The gain control circuitincludes a potentiometer resistor 243 in the output circuit of thepush-pull amplifier |8|. The delayed waves D and D are applied to theopposite ends of the resistor 243. An adjustable differential gainbalance tap on resistor 243 may be moved to either side of the centerthereof to decrease the gain of the I.F. ampliier |62 during either thereceptionof the pulse A or the pulse B. Thevoltage at the gain balancetap is supplied through a resistor 244 and a capacitor 246 to the anodeof a, diode 241 and to the #2 and #3 contact points of a. diii'erentialgain control switch 248. Thus when the receiver is on either the #2 or#3 operation position for pulse alignment on the fast sweeps, thediierential gain control voltage is applied through the switch 248 and aconductor 249 to the gain control grid of an ampller tube in the I.F.amplier |62.

The differential gain the receiver on either is as follows:

When the gain balance tap ls at the center of resistor 243, the waves Dand D' balance or cancel each other at the tap and no voltage wave isapplied to the diode 241. When the tap is on the upper side of thisbalance position, a Wave of one polarity, that of wave D', is applied tothe diode 241; when the tap is on the lower side of 'the balance point,a wave of the opposite polarity, that of wave D, is applied to the diode241. The diode 241 functions to supply a negative bias during thenegative half cycle following a positive For example, if the appliedwave corresponds to wave D', the positive half cycle causes diodecurrent to charge capacitor 246, and during the following negative halfcycle the capacitor 246 discharges slowly through a resistor 25|connected across the diode 241 thus making the anode of diode 241negative with respect to ground and reducing the gain of the I.F.amplifier |62 while the B pulse is being amplified.

It will be apparent that by delaying the waves D and D there is avoidedthe possibility of transient voltages causing a disturbance in the I.F.amplifier |62 during the amplication of thepulse A" or the pulse B,"such transient voltages being produced when the waves D and D' changefrom positive to negative polarity or vice versa. Likewise, switchingdisturbances in the mixer tubes |18 and |19 during the fast sweeps f-gand h-i are avoided.

With switch 248 on the #1 operation position for pulse alignment, normaloperating bias is on the switch 248 on control operation with #2 or #3operation position A AND B PULSE DRIFT CONTROL The apparatus illustratedin Fig. l includes three control elements for causing the received A andB pulses to drift to the right or to th'e left amasar on the cathode-raytraces during the pulse alignment procedure. Two of these have alreadybeen described, one of them being the right-drift switch 96 associatedwith the station selector switch-to give fast drift to the right, andthe other being the control knob l I of the oscillator ill which may beadjusted to give a slow drift either to the right or to the left.

The third drift control element is a left-drift switch 253 for providinga fast drift to the left. This left drift of the A and B pulses isobtained by supplying the wave H from the mixer lill over a conductor254 and through a resistor 256 and a capacitor 251 to a contact point ofthe switch 253. The wave H is then applied to the blocking oscillator I2when the switch 253 is inthe left-drift position. The negative polarityportions of the wave H block the oscillator l2 while they are on thegrid of th'e oscillator, thus allowing the blocking oscillator I5to rununkeyed for a fraction of the time, and thereby increasing averagerepetition period to produce the desired drift.

PROCEDURE IN MAKING A TIME MEASURE- MENT The successive steps in makinga measurement of the time interval between the A and B pulses 'from apair of ground stations will now be described.

ALromrEN'r or A arm B Ponsas Position #1 stationary on the two traces,which atthis time are of equal length. Th'e pulses A and B appear on thetraces in some such relation as shown in Fig. 2. At this point it is notknown which one of the pulses is on a particular trace. To determinethis, a drift switch is operated to drift both pulses onto the trace a-bwith one pulse on the left end of the trace. The first occurring pulse,i. e., the left one is the B pulse. That this is true will be evident byreferring to Fig. 10 and by assuming that the starting time t of theslow-sweep wave c--d is at the mid-point of the defiecting wave cycle,the condition for equal length traces.

Next the starting time t oi the sweep wave c-d (Fig. 10) is advanced byoperating the controls H12' and |06' of the variable delay circuits liliand |06 (Fig. 1) to make the A pulse fall on the upper trace c-d andalso to make it align approximately, at least, with the B pulse as shownin Fig. 4.

PositO'n #2 Position #3 The nal alignment of the A and B pulses is doneon operation position #3 with th'e two traces superimposed as shown inFig. 7. The front edges of the A and B pulses are exactly aligned (theyusually dier slightly in shape) by operating the knob |06' of the netiming adjustment circuit B06 (Fig.1). The time reading can now be made.

Tna Tmp DIFFERENCE Rsnnmcs Y Position' #4 Having aligned the A and Bpulses, the receiver is switched to the #4 slow-sweep operation positionwhereby the 1000 as. timing marks appear on the cathode-ray tube screen(in the up direction from the traces) as shown in Fig. 8 while 50 as.and 10as. marks may appear on the screen (in the down direction) theyare too closely spaced to be counted. The marks on the lower trace a-bare ignored. The full 1000 as. intervals are found by counting all the1000 as. timing spaces on the upper trace c-v-d' (this being theunblanked portion of the trace c-d). Fig. 11 shows the relationship ofthe deiiecting wave c-d, the blanking wave L and the 1000 as. timingmarks, and by graphical construction shows the resulting trace c-d' andthe timing marks thereon.

Figs. 8 and 11 do not illustrate the same time reading; the reading inFig. 8 being seven 1000 as. spaces or 7000 microseconds plus afractional interval, and the reading in Fig. ll being four 1000 as.spaces or 4000 microseconds plus a fractional interval. Note is made ofthe fact that the 1000 ps. mark coinciding with the right-hand end d' ofthe trace is not counted (as there is one more mark than integralspaces) and there-V fore it may be blanked out. if desired.

Position #5 For the final time reading the receiver is switched .to the#5 fast-swee operation position whereby the 1000 as. and 1 0 as. timingmarks appear in the up direction on the upper trace h-fi and whereby the500 as. marks and th'e 50 as. marks (one of the 50 as. marks being thecrosshair mark) appear also in the up direction on the lower trace f-gas shown in Fig. 9. Due to the 50 as. and l0 ns. pulses applied to thelower plate |68, 50 as and l0 as. marks appear in the -down direction onboth traces. The as. and 10 as. intervals are obtained by counting(right to left) from and including the rst 1000 as. marker appearing tothe right of the crosshair mark. The cross-hair mark is the second 50ps. mark from the left on the lower trace f-g. The reason for includingthe 1000 as. marker in the count is explained hereinafter. Only one 1000as. marker appears in the example shown in Fig. 9 but two of them mayappear.

The reading in the example of Fig. 9 for 100 as. intervals is 2, and for10 as. intervals (counting from the rst 100 as. mark to the right of thecross-hair) is 6. The number of microseconds in units between the last10 as. mark and the crosshair is estimated at 5 as. Thus, the reading inposition #5 for the example of Fig. 9 is 265 ps.

The complete reading for the example illustrated in Figs. 8 and 9 is7265 as.

At rst glance it would appear that, in counting the 100 ps. intervals,the first mark to be counted should be the-first 100 ps. marker to theleft of the 1000 as. mark from which the count starts. The reason forincluding the said 1000 ps. mark in the count is that this adds a 100ps. interval at the start of the count to make up for the loss of a 100as. interval at the end of the count. The loss of an interval is due tothe fact that the 50 as. mark which is utilized as the cross-hair is 100ps. fromvthe start of the trace fg. This will be better understood byreferring to Fig. 11.

l Fig. 11 shows the relationship of the fast-sweep f 19 delecting wavesf-g and h-- and the timing marker pulses (the as. pulses -belngomitted), and by graphical construction shows the resultting. traces h-iand f-g and the timing and cross-hair marks thereon.

The iirst feature to be noted in Fig. 11 is that the fast-sweep wave h-ioccurs during the fractional 1000 as. interval of the count that wasmade with the receiver in the #4 operation position. This fractionalinterval could be found accurately merely by counting 100 as, and 10 as.timing marks on the resulting trace h-i (i. e.. counting from the 1000as. mark at the start of said interval over to the left end oi the tracelli-i) if the wave h-i (also the wave f-gl started at the time t withsuilicient expansion and also gave a well defined trace at the start. Amore desirable procedure is to generate the wave h-i and f-g asdescribed and count the timing marks on the upper trace h-i over to across-hair mark on the lower trace fg, this being the second 50 as. markfrom the left end of said trace. Thus, any necessity for reading markson the first 100 as. portion of the fastsweep traces is avoided. Aspreviously stated, the 100 ps. interval lost by counting to thecrosshair mark instead of to the end of the trace is added at the startof the count by counting the 1000 as. mark as a 100 as. interval.

The fractional interval count illustrated in Fig, 11 is 445 as. Thecomplete count illustrated in this figure, therefore. is 4445 as.

CHECKING OF COUNTER OPERATION The reason for applying 500 as. pulsesfrom the lead |80 to the mixer tube |19 is to produce a 500 ps. mark onthe lower fast-sweep trace f-g so that the operator may determinewhether the counter feed-back circuits for station selection areoperating properly. As previously explained, at 0 station position notime intervals are subtracted; at #1 station position, a 50 as. intervalis substracted: at #2 station position, a 100 as. interval issubtracted, etc. These intervals are subtracted at the beginning of boththe upper sweep trace and the lower sweep trace and vary from a total of50 as. on #l station position to 350 as, on #7 station position.

To make a check on the feed-back operation, the 50 as. pulses on thelower trace f-g are counted from the cross-hair mark to the first 500as. mark (counting left to right). On the 0 station position, betweenthese two marks there should be eight 50 as. intervals or seven 50 as.marks, the eight 50 as. mark coinciding with the 500 as. mark. On the #1station position there should be six 50 as, marks, on the A#2 stationposition five 50 ys. marks, etc. If when the station selection switch ison the #2 position, for example. a check shows a number of 50 as. marksother than five, then the operator knows that he must adjust thefeed-back circuit to avoid selecting the wrong pair of ground stations.

We claim:

1. In a radio navigation system wherein a pair of from a pair of spacedsynchronized radio ground stations are received to determine the timedifference of said pair of pulses at the point of reception and therebylocate a position line for the point of reception, means including acathode ray tube and a comparatively slow-sweep deflection circuit fordetermining or indicating said time difference in terms of timeintervals of a certain duration within a fractional part of oneperiodically recurring radio pulses transmitted of said time intervals,means including a comparatively fast sweep deection circuit fordeflectlng the cathode ray of said cathode-ray tube during saidfractional part of a time interval and for determining or indicatingsaid fractional part of a time interval in terms of smaller timeintervals, and means for selectively switching either of said timedetermining means to an operating condition.

2. The invention according to claim 1 wherein said fast-sweep deflectioncircuit is designed to produce a defiecting wave that defiects saidcathode ray first rapidly and then comparatively slowly to produce atrace that is expanded at its start.

3. In a radio navigation of periodically recurring transmitted from apair radio ground stations,

system wherein a pair radiopulses A and B of spaced synchronizedrespectively, are received to determine the time difference of said pairof pulses at the point of reception and thereby locate a position linefor said point of reception, and wherein said A pulse precedes themid-point of the B pulse period by a predetermined amount at the pointsof transmission, means including a cathode ray tube and a comparativelyslow-sweep deflection circuit for determining or indicating the numberof whole time intervals of a certain duration in the time period betweensaid midpoint of the B pulse period and the A pulse, there being afractional part of one of said time intervals at the beginning of saidtime period that is yet to be determined in terms of smaller timeintervals, means including a comparatively fastsweep deflectioncircuitfor deecting the cathode ray of said cathode ray tube during saidfractional part of a time interval for determining or indicating saidfractional part of a time interval in terms of smaller time intervals,and means for selectively switching either of said time determiningmeans to an operating condition,

4. In a radio navigation system wherein a pair of periodically recurringradio pulses A and B transmitted stations, respectively, are received todetermine the time difference of said pair of pulses at the point ofreception and thereby locate a position line for said point ofreception, and wherein said A pulse precedes the mid-point of the Bpulse period by a predetermined amount at the points of transmission,means including a cathode ray tube and a comparatively slow-sweepdeection circuit for determining or indicating the number of whole timeintervals of a certain duration in the time period between said midpointof the B pulse period and the A pulse, there being a fractional part ofone of said time intervals at the beginning of said time period that is.

yet to be determined in terms of smaller time intervals, means includinga comparatively fastsweep deflection circuit for defiecting the cathoderay of said cathode ray tube during said fractional part of a timeinterval for determining or indicating said fractional part of a timeinterval in terms of smaller time intervals, said fastsweep circuitbeing designed to produce an expanded trace by deilecting the cathoderay of said tube i'lrst rapidly and then more slowly, and means forselectively switching either of said time determining means to anoperating condition.

5. In a radio navigation system wherein a pair of periodically recurringradio pulses A and B transmitted from a pair of spaced synchronizedradio ground stations, respectively, are received to determine the timedifference of said pair oi' pulses and thereby locate a position linefor the point of reception, said A pulse preceding the mid-point of theB pulse period by a predetermined amount at the points of transmission,means including a cathode ray tube and a com-V paratively slow-sweepdeflection circuit for producing pairs of slow-sweep traces having thesame -repetition rate as said B pulses, means for making a pair of A andB pulses appear on at least one of said traces. means including a timingpulse generator connected to produce timing marks spaced by timeintervals of like duration on at least one of said traces for indicatingthe number of whole time intervals of said duration in the time periodbetween said mid-point of the B pulse period and the A pulse, therebeing a fractional part of one of said time intervals-at the beginningof said time period that is indicated only approximately, meansincluding a comparatively fast-sweep deflection circuit for deiiectingthe cathode ray of said tube successively for producing pairs offast-sweep traces having the same repetition rate as said B pulses andwith the fastsweep deflection that produces one of said fastsweep tracesoccurring during said fractional part of a time interval. means formaking a pair of A and B pulses appear on the two traces,.respectively,of said pair of fast-sweep traces. means including said timing pulsegenerator for putting timing marks which are spaced by smaller timeintervals than said first-mentioned time interval on said fast-sweeptraces lwhereby said fractional part of a time interval may bedetermined from the smaller time-interval marks produced by the timingpulses occurring during said fractional part of a time interval, andmeans -for selectively switching either of said time determining meansto an operating condition.

6. The invention according to claim wherein said fast-sweep deflectioncircuit is designed to produce a deflecting wave that deects saidcathode ray first rapidly and then comparatively slowly to produce atrace that is expanded at its start.

7. The method of measuring the time relation of one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both groups of receivedpulses have Vthe same repetition period and where said groups areproduced by transmitting periodically recurring pulses A and B from apair of spaced synchronized radio ground stations, respectively, said Apulse preceding the mid-point of the B pulse period by a predeterminedamount at the points of transmission. said method comprising the stepsof producing two successive slow-sweep cathode-ray defiecting waves,said pair of deecting waves having a total repetition period equal tothat of said groups of received pulses, producing groups of timingpulses each group having a diil'erent repetition period and having afixed time relation to the start and finish of the cycle of said twodeiecting waves, causing each of said deecting waves to produce a slowcathode-ray trace upon at least one of which a group of said timingpulses may be made to appear, also producing two successive fast-sweepcathode ray deflecting waves each starting from the same voltage leveland each of identical slope and having a total repetition period equalto that of said groups of received pulses, causing each of saidfast-sweep deiiecting waves to produce a cathode-ray trace and causing areceived pulse of each group of received pulses to appear on said twofast-sweep cathode- 22 ray traces, respectively, advancing the start ofthe second fast-sweep detlecting wave of said cycle with respect to themid-point in the full deilecting wave. cycle until said received pulseson said fast-sweep traces are in exact alignment or coincidence, causethe timing marks having one of the longer repetition periods to appearon at least one of said slow-sweep traces and counting saidlast-mentioned timing marks from a point corresponding to the mid-pointof said deflecting wave cycle to that one of said last-mentioned markswhich occurs immediately following an A pulse to determine within acertain fractional time interval of said longest repetition period theamount of time that the start of said second fast deectlng wave isadvanced with respect to said mid-point, causing the pulse correspondingto said last-counted timing mark immediately following the A pulse andalso at least one group of pulses having a shorter repetition periodthan said longer repetition period to appear as timing marks on thefast-sweep trace produced by said second fast-sweep deecting wave,causing a timing pulse from one of said groups having one of the shorterrepetition periods to appear as a cross-'hair mark on the first part ofthe trace produced by the first fast-sweep deecting wave, and countingtiming marks on the trace produced by said second fast-sweep wave fromthe mark' produced thereon by the pulse corresponding to saidlast-counted timing mark to said cross-hair Vmark on said iirstfast-sweep trace to determine said fractional time interval.

8. In a navigation system wherein periodically recurring radio pulsesare radiated from A and B ground stations as A and B pulses,respectively, with the B pulses occurring at a predetermined timefollowing the mid-point of the period of the A pulses, the method ofmeasuring the time interval between the A and B pulses as they appear ata point remote from said ground stations which comprises receiving saidA and B pulses at said point, producing pairs of periodically recurringpulses, the second pulse of the pair being adjustable in time withrespect to the first pulse of the pair, successively producing pairs ofsequentially occurring slow-sweep deecting waves, at least the firstwave of the pair occurring in a xed time relation to the rst of saidpair of pulses, deflecting a cathode ray successively by said waves toproduce two parallel adjacent cathode-ray traces, causing said A and Bpulses to appear on said traces, establishing a certain time relationbetween the B pulse and a time reference point, adjusting the timing ofsaid adjustable pulse to establish the same time relation between the Apulse and said adjustable pulse as said previously established timerelation between the B pulse and its time reference point, successivelyproducing pairs of sequentially occurring fast-sweep deecting waveshaving decreasing slope from at least near the start of the wave andwhich are identical throughout their useful deflecting portions, thei'lrst wave in each pair of fast-sweep waves starting at the same timeas the first Wave in each pair of slow-sweep waves, the start of thesecond fast-sweep wave being initiated by said adjustable pulse,deflecting said cathode ray successively by said fast-sweep waves toproduce two parallel' adjacent cath-ode-ray traces whereby said A and Bpulses appear on said two fast-sweep traces with the A pulse on thetrace that is produced by the second of said pair of fast-sweep waves,and producing timing marks on a trace produced by one of said slow- 23sweep deecting waves and on the traces produced by said fast-sweepdeiiecting waves whereby the time difference between a time referencepointand the starting time of said adjustable pulse may be determined.

9. In a navigation system wherein periodically recurring radio pulsesare radiated from A and B ground stations as A and B pulses,respectively, with the B pulses occurring at a predetermined timefollowing the mid-point of the period of the A pulses, a receiver forreceiving said A and B pulses, a cathode-ray deecting circuit forproducing successively pairs of sequentially occurring slow-sweepdeecting waves, a second cathode-ray deiiecting circuit for producingsuccessively pairs of sequentially occurring identical fast-sweepdeilecting waves having decreasing slope from at least near the start ofthe wave, means for deecting a cathode ray by said slowsweep waves toproduce two parallel adjacent slow-sweep cathode-ray traces and fordeiiect- `ing it by said fast-sweep waves to produce two paralleladjacent fast-sweep cathode-ray traces which are expanded at one end,means for adjusting the starting time of the second of said pair offast-sweep deflecting waves, means for causing said A and B pulses toappear on said two fast-sweep traces with the A pulse on the trace thatis produced by said second fast-sweep detlecting wave whereby said A andB pulses may be aligned by adjusting said starting time, and meanscomprising a chain of frequency dividers for producing timing pulsesincluding groups of 1000 ps., 100 as. and 10 lis. timing pulses, andmeans for causing said 1000 lis. timing pulses to produce timing markson at least one of said slow-sweep traces whereby said 1000 as. marksmay be counted to determine the time relation of said A and B pulses toa fractional 1000 as. interval, means for causing the 1000 ps. timingpulse that is adjacent to said fractional interval, and also the 100 as.timing pulses and the 10 as. timing pulses to produce timing marks onthe fast-sweep trace which is produced by the second fast-sweepdeilecting wave, and means for causing a timing pulse to produce a.timing mark on the expanded end of the other fast-sweep trace andextending toward the trace produced by said sec-ond fast-sweep wavewhereby it may be utilized as a fixed position cross-hair mark incounting timing marks appearing on the fastsweep adjustable trace.

10. The invention according to claim 9 wherein means is also providedfor producing 500 as. timing pulses and means for causing them toproduce timing marks on said other fast-sweep trace which is produced bythe rst fast-sweep deilecting wave whereby the operation of said chainof frequency dividers may be checked by counting said 500 as. timingmarks,

1l. In a navigation system wherein periodically recurring radio pulsesare radiated from A and B ground stations as A and B pulses,respectively, with the B pulses occurring at a predetermined timefollowing the mid-point of the period of the A pulses, a receiver forreceiving said A and B pulses, a cathode-ray deflecting circuit forproducing successively at a certain repetition period pairs ofsequentially occurring slow-sweep deflecting waves, a second cathode-raydefiecting circuit for producing successively at said repetition periodpairs of sequentially occurring identical fastsweep deilecting waveshaving decreasing slope from at least near the start of the wave, meansfor detiecting a cathode ray by said slow-sweep waves 24' to produce twoparallel adjacent slow-sweep cathode-ray traces and for detlecting it bysaid fast-sweep waves to produce two parallel adjacent fast-sweepcathode-ray traces which are expanded at one end, means for adjustingthe starting time of the second of said pair of fast-sweep detlectingwaves, means for causing said A and B pulses to appear on said twofast-sweep traces with the A pulse on the trace that is produced by saidsecond fast-sweep detlecting wave whereby said A and B pulses may bealigned by adjusting said starting time, and means for producing timingpulses each having a repetition period that is a sub-multiple of saidrepetition period of the detlecting waves and including groups of 1000as., ps, and 10 as. timing pulses, and means for causing said 1000 ps.timing pulses to produce timing marks on at least the second of saidslowsweep traces whereby said 1000 as. marks may be counted to determinethe time relation of said A and B pulses to a fractional 1000 iis.interval. means for causing the 1000 fis. marker pulse that is adjacentto said fractional interval. and also the 100 ps. marker pulses and the10 as. marker Y pulses to produce timing marks appearing on thefast-sweep trace that is produced by the second fast-sweep deilectingwave and means for causing a timing pulse to produce a timing mark onthe expanded end of the `other fast-sweep trace and exten-dingsubstantially to the trace produced by said second fast-sweep wavewhereby it may be utilized as a fixed position cross-hair mark incounting timing marks appearing on the fastsweep adjustable trace.

12. In a navigation system wherein periodically recurring radio pulsesare radiated from A and B ground stations as A and B pulses,respectively, with the B pulses occurring at a predetermined timefollowing the mid-point of the period of the A pulses, a receiver forreceiving said A and B pulses, a cathode-ray deiiecting circuit forproducing successively pairs of sequentially occurring slow-sweepdeiiecting waves, a second cathoderay deecting circuit for producingsuccessively pairs of sequentially occurring identical fastsweepdefiecting Waveshaving decreasing slope from at least near the start -ofthe wave, means for deecting a cathode ray by said slow-sweep waves toproduce two parallel adjacent slow-sweep cathode-ray traces and fordeecting it by said fast-sweep waves to produce two parallel adjacentfast-sweep cathode-ray traces which are expanded at one end, means foradjusting the starting time of the second of said pair of fastsweepdeflecting waves, means for causing said A and B pulses to appear onsaid two fast-sweep traces with the A pulse on the trace that isproduced by said second fast-sweep deflecting wave whereby said A and Bpulses may be aligned by adjusting said starting time, and means forproducing timing pulses including groups of 1000 lis., 100 ps. and 10as. timing pulses, and means for causing said 1000 as; timing pulses toproduce timing marks on at least one of vsaid slow-sweep traces wherebysaid 1000 as, marks may be counted to determine the time relation ofsaid A and B pulses to a fractional 1000 as. interval, means for causingthe 1000 as, marker pulse that is adjacent to said fractional interval,and also the 100 as. marker pulses and the 10 ps. marker pulses toproduce timing marks appearing on the fast-sweep trace produced by thesecond fastsweep deecting wave and means for producing 50 as. timingpulses and causing them to produce timing marks on the other fast-sweeptrace with one of the 50 ps. marks appearing on the expanded end of saidother fast-sweep trace and extending substantially to the trace producedby said second fast-sweep wave whereby said one 50 as. mark may beutilized as a -xed position cross-hair mark in counting timing marksappearing on the fast-sweep adjustable trace.

13. Apparatusl for measuring the time relation of one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both groups of pulses havethe same repetition period, comprising means for producing twosuccessive slowsweep cathode-ray deecting waves starting at the samevoltage level and each of identical slope and having a total repetitionperiod equal to that of said groups of pulses, means for producinggroups of timing pulses each group having a different repetition periodand having a fixed time relation to the start and linish of the cycleAof said two deiiecting waves, means including an operation positionswitch for causing each of said deecting waves to produce a cathode-raytrace and means for causing a pulse of each group of received pulses toappear on atleast one of said two cathode-ray traces, means forproducing two successive fast-sweep cathode-ray denecting waves Y eachstarting from the same voltage level and each of identical slope and thetwo fast-sweep waves having a total repetition period equal to that ofsaid received pulses, means including said operation position switch forcausing each of said fast-sweep deecting waves to produce a cathode-raytrace and means for causing a pulse of each group ofreceived pulses toappear on said two fast-sweep cathode-ray traces, respectively, meansfor changing the start of the second fastsweep deecting wave of saiddefleoting Wave cycle until said received pulses on said traces are insubstantially exact alignment or coincidence, switching means forcausing at leas't one of the longer-repetition-period groups of timingpulses to produce timing rnarks on at least one of said slow-sweeptraces whereby from the Aresulting timing marks an operator maydetermine within a fraction of said longer repetition period or intervalthe amount that the start of said second fastsweep wave is shifted intime with respect to said mid-point of the full deflecting wave cycle,switching means for causing at least two of said groups of timing pulsesand the longer-repetitionperiod pulse adjacent to said fractionalinterval to produce timing marks on the fast-sweep trace produced bysaid second fast-sweep defiecting wave and for causing a timing pulsehaving a repetition period less than said longer repetition period toappear as a cross-hair mark on the trace produced by the rst fast-sweepdeecting wave, whereby an operator may count from the timing markproduced on the second fast-sweep trace by said pulse adjacent to saidfractional interval over to said cross-hair mark to determine saidfractional interval, said fast-sweep waves being shaped to expand thefast-sweep traces in the region of said fractional repetition period ascompared with the remaining portions of the fastsweep traces.

14. In a navigation system wherein periodically recurring radio pulsesare radiated from A and B ground stations as A and B pulses,respectively, with the B pulses occurring at a predetermined timefollowing the mid-point of the period of the A pulses, the method ofmeasuring the time interval between the A and B pulses as they appear ata point remote from said ground stations which 26 comprises receivingsaid A and B pulses at said point, successively .producing pairs 'ofsequentially occurring slow-'sweep deeoting waves, and produclng aperiodically recurring pulse that is adjustable in time with respect tothe rst of said slow-sweep waves, derlecting a cathode ray successivelyby said waves to produce two parallel adjacent cathode-ray traces,causing said A and B pulses to appear on at least one of said traceswith the B pulse near the start of the trace produced by the rst wave ofsaid pair, thereby establishing a certain time relation between the B.pulse and a time reference point, adjusting the timing of saidadjustable .pulse to establish the same time relation between the Apulse and said adjustable pulse as said previously established timerelation between the B pulse and its time reference point, successivelyproducing pairs of sequentially occurring fast-sweep deecting waveshaving decreasing slope from at least near the start of the waveandwhich are identical throughout their useful deflecting portions, thestart of the second fast-'sweep wave being initiated by said ad-`instable pulse, deectlng sai-d cathode ray successively by saidfast-sweep waves to .produce two parallel adjacent fast-sweep Vcathode-ray traces whereby said A and B' pulses appear on said twotraces with the A pulse on the trace that is produced by the second ofsaid pair of deecting waves, and producing timing marks on at least oneof the traces produced by said slowsweep deliecting waves and also onthe traces produced by said fast-sweep deflecting waves whereby the timedifference between a time reference point and the starting time of saidadjustable pulse may be determined. Y

15. The method of measuring the time relation of one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both groups of pulses havethe same repetition period, said method comprising the steps ofproducing two successive slow-sweep cathode ray deflecting waves eachstarting from the same voltage level and each of identical slope but ofadjustable duration and having a total repetition period equal to thatof said received pulses, producing groups of timing pulses having aiixed time relation to the start and nish of the cycle of said twodenecting waves, the repetition period of each group of timing pulseshaving a decimal relation to the repetition periods of the other groupsof timing pulses causing each of said deflecting waves to produce a slowcathode-ray trace and causing a received pulse of each group of receivedpulses to appear on said two cathode-ray traces, respectively, changingthe start of the second deflecting wave of said cycle with respect tothe mid-point of the full deilecting Wave cycle until said pulses onsaid traces are approximately in alignment or coincidence, alsoproducing two successive fast-sweep cathode-ray deiiecting waves eachstarting from the same voltage level and each of identical slope and thetwo fast-sweep waves having a total repetition period equal to that ofsaid received pulses, causing each of said fast-sweep deiiecting wavesto produce a cathoderay trace and causing a pulse of each group ofreceived pulses to appear on said two fast-sweep cathode-ray traces,respectively, changing the start of the second fast-sweep deiiectingwave of said deecting wave cycle with respect to said mid-point of thefull denecting wave cycle until said received pulses on said traces arein substantially exact alignment or coincidence, caus- 27 ing at leastone of said groups of timing pulses to produce timing marks on at leastthe second of said slow-sweep traces, blanking out said seconddefiecting wave from said mid-point to the end of said cycle whereby thetiming marks on the remainder of the slow-sweep trace produced by saidsecond defiecting wave indicate within a certain fractional timeinterval the amount of ftime that the start of said second slow-sweepwave is shifted with respect to said mid-point of the'full defiectingwave cycle, causing at least two of said groups of timing pulsestoproduce timing marks on the fast-sweep trace produced by said secondfast-sweep defiecting wave, causing a timing pulse from the one of saidtwo groups having the longer repetition period to appear as a cross-hairmarker on the trace produced by the first fast-sweep defiecting wave,and counting from a. certain timing marker on the trace produced by saidsecond fast-sweep wave to said cross-hair marker to determine saidfractional time interval, said certain timing marker being the oneproduced by the iirst occurring longer-repetition-period pulse whichfollows in time sequence the pulse producing saidb cross-hair marker andwhich is the same pulse that produces the first occurring timing mark onsaid remainder of the slow-sweep trace.

16. In a system for measuring the time relation of one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both 'groups of pulses havethe same repetition period, said system comprising means for producingtwo successive slow-sweep cathode-ray deecting Waves each of identicalslope and starting from the same voltage level, said pair of waveshaving a repetition period equal to that of said received pulses, meansfor producing groups of timing pulses having a fixed time relation tothe start and finish of the cycle of said pair of defiecting waves, therepetition period of the several groups of timing pulses having adecimal relation to each other, means for causing each of said slowsweepdefiecting waves to produce a slow-sweep cathode-ray trace and means forcausing a ypulse of each group of received pulses to appear on said twoslow-sweep cathode-ray traces, respectively, means for changing thestart of the second slowsweep defiecting wave of said cycle with respectto themid-point of said cycle until the received pulses on said tracesare approximately in alignment or coincidence, means for also producingtwo successive fast-sweep cathode-ray defiecting waves each startingfrom the same voltage Ilevel and each of identical slope, said pair offastsweep waves having a repetition period equal to that of saidreceived pulses, means for causing each of said fast-sweep defiectingwaves to produce a cathode-ray trace and means for causing a pulse ofeach group of received pulses to appear on said two fast-sweepcathode-ray traces, respectively, means for changing the start of thesecond fast-sweep deecting wave of said defleeting wave cycle withrespect to said mid-point of the full defiecting wave cycle until saidreceived pulses on said traces are in substantially exact alignment orcoincidence, means for causing at least one of said groups of timingpulses to produce timing marks on at Ileast the second of saidslow-sweep traces, means for blanking out said second defiecting wavefrom said mid-point to the end of said cycle whereby the timing marks onthe remainder of the slow-sweep trace produced by said second deectingwave indicate 'amount of time that the start of said second slowsweepwave is shifted with respect 4to 4said midpoint of the full deilectingwave cycle, means for causing at least two of said groups of timingpulses to produce timing marks on the fast-sweep trace produced by saidsecond fast-sweep defiecting wave, means for causing a timing pulse fromthe one of said two groups having the longer repetition period to appearas a cross-hair marker on the trace produced by the first fast-sweepdeilecting wave, whereby an operator. may count from a certain timingmarker on the trace produced by said second fast-sweep wave to saidcross-hair marker to determine said fractional time interval, saidcertain timing marker being the one produced by the rst occurringlongerrcpetition-period pulse which follows in time sequence the pulseproducing said cross-hair marker and which is the same pulse thatproduces the first occurring timing mark on said remainder of theslow-sweep trace.

17. In a system for measuring the time relation of one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both groups of pulses havethe same repetition period, said system comprising means for producingtwo successive slow-sweep cathode-ray defiecting waves each of identicalslope and starting from the same voltage level, said pair of waveshaving a repetition period equal to that of said received pulses, meansfor producing groups of timing pulses having a fixed time relation tothe start and iinish of the cycle of said pair of defiecting waves, therepetition period of the several groups of timing pulses having adecimal relation to each other, means for causing each of saidslow-sweep defiecting waves to produce a slow-sweep cathoderay trace andmeans for causing a pulse of each group of received pulses to appear onsaid two slow-sweep cathode-ray traces, respectively, means for changingthe start of the second slowsweep defiecting wave of said cycle withrespect to the mid-point of said cycle until the received pulses on saidtraces are approximately in alignment or coincidence, means for alsoproducing two successive fast-sweep cathode ray defiecting waves eachstarting from the same voltage level I and each oi' identical slope,said pair of fastsweep waves having a repetition period equal to that ofsaid received pulses, means for causing each of said fast-sweepdefiecting waves to produce a cathode-ray trace and means for causing apulse of each Agroup of received pulses to appear on said two fast-sweepcathode-ray traces. respectively, means for changing the start of thesecond fast-sweep defiecting wave of said deflecting wave cycle withrespect to said mid-point of the full defiecting wave cycle until saidreceived pulses on said traces are in substantially exact alignment orcoincidence, means for causing at least one of said groups of timingpulses to produce timing marks on at least the second of said slow-sweeptraces, means for blanking out said second defiecting wave from saidmid-point to the end of said cycle whereby the timing marks on theremainder of the slow-sweep trace produced by said second deecting waveindicate within a certain fractional time interval the amount of timethat the start of said second slow-sweep wave is shifted with respect tosaid mid-point of the full defiecting wave cycle, means for causing atleast'two of said groups of timing 29 pulses to produce timing marks onthe fast-sweep trace produced by said second fast-sweep deiiecting wave,means for causing a timing pulse from the one of said two groups havingthe longer repetition period to appear as a cross-hair marker on thetrace produced by the rst fast-sweep deecting wave, whereby an operatormay count from a certain timing marker on the trace produced by saidsecond fast-sweep wave to said cross-hair marker to determine saidfractional time interval, said certain timing marker being the oneproduced by the rst occurring longerrepetition-period pulse whichfollows in time sequence the pulse producing said cross-hair marker andwhich is the same pulse that produces the rst occurring timing mark onsaid remainder of the slow-sweep trace, said means for changing thestart of the slow deecting wave comprising means for changing the timingof the edge of a pulse. the start oi both the slow deilecting wave andthe fast deecting wave beginning 'in response to the occurrence of saidpulse edge, and switching means for selectively causing said pulse edgeto initiate either the slow-sweep wave or the fast-sweep wave.

18. The method of measuring the time relation of one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both groups of pulses havethe same repetition period, said method comprising the steps ofproducing two successive slow-sweep cathode-ray deflecting waves eachstarting from the same .voltage level and each of identical slope but atleast one of which having a duration that changes with a change in thestarting time of the other of said pair of waves having a totalrepetition period equal to that of said groups of received pulses,producing groups of timing pulses having a xed time relation to thestart and finish of the cycle of said two deflecting waves each group ofpulses having a different repetition rate, causing each of saiddefiecting waves to produce a slow-sweep cathode-ray trace and causing apulse of each group of received pulses to appear on said two cathode-raytraces, respectively, changing the start of the second slow-sweepdeflecting wave of said cycle with respect to the mid-point of the fulldeecting wave cycle until said pulses on said traces are approximatelyin alignment or coincidence, also producing two successive fast-sweepcathode-ray deficcting waves each starting from the same voltage leveland each of identical slope, said slope being of gradually decreasingsteepness from the start to the end of the wave, the two fast-sweepwaves having a total repetition period equal to that of said receivedpulses, causing each of said fast-sweep deflecting waves to produce acathode-ray trace and causing a pulse of each group of received pulsesto appear on said two fast-sweep cathode-ray traces, respectively,changing the start of the second fast-sweep defiecting wave of saiddeiiectng wave cycle with respect to said mid-point of the fulldeflecting wave cycle until said received pulses on said traces are insubstantially exact alignment or coincidence, causing at least one ofsaid groups of timing pulses to produce timing marks on at least thesecond of said slow-sweep traces, blanking out said second deflectingwave from said mid-point to the end of said cycle whereby the timingmarks on the remainder of the slow-sweep trace produced by said seconddeilecting wave indicate within a certain fractional time interval Y 30the amount ot time that the start of said second slow-sweep wave isshifted with respect to said mid-point ofthe full deflecting'wave cycle,causing lat least two of said groups of timing pulses to produce timingmarks on the fast-sweep trace produced by said second fast-sweepdeecting wave, causing a timing pulse from the one o! said two groupshaving the longer repetition period to appear as a cross-hair marker onthe trace produced by the first fast-sweep deflecting wave, and

counting from a certain timing marker on the trace produced by saidsecond fast-sweep wave to said cross-hair marker to determine saidiractional time interval, said certain timing marker being the oneproduced by the iirst occurring longer-repetition-period pulse followingin time sequence the pulse producing said cross-hair marker and beingone that coincides in time with the marker pulse that marks the end ofsaid fractional time interval and the beginning of the next adjacentfull time interval counted on the slow Sweep.

19. 'Ihe method of measuring the time relation of .one group ofperiodically recurring received pulses with respect to another group ofperiodically recurring received pulses where both groups of receivedpulses have the same repetition period and where the pulses of one grouphave a staggered time relation with respect to the pulses of the othergroup, said method comprising the steps of producing two successiveslow-sweep cathoderay deiiecting waves, said pair of deflecting waveshaving a total repetition period equal to that of said groups ofreceived pulses, producing groups of timing pulses each group having adifferent repetition period and having a xed time relation to the startand nish of the cycle of said two deecting waves, causing each of saiddeilecting waves to produce a slow cathode-ray trace upon at least oneof which a group of said timing pulses may be made to appear, alsoproducing two successive fast-sweep cathode-ray deflecting waves each ofwhich starts simultaneously with the startsof said two slow-sweep waves,respectively, each starting from the same voltage level, and each ofidentical slope and having a total repetition period equal to that ofsaid groups .of received pulses, causing each of said fast-sweepderlecting waves to produce a lcathode-ray trace and causing a pulse ofeach group of received pulses to appear on said two fast-sweepcathoderay traces, respectively, advancing the start of the secondfast-sweep deflecting wave of said cycle with respect to the mid-pointof the full defiecting wave cycle until said received pulses on saidtraces are in exact alignment or coincidence, causing the timing markshaving one of the longer repetition periods to appear on at least thesecond of said slow-sweep traces and counting said last-mentioned timingmarks from a certain last occurring mark to a certain rst occurring markto indicate within a certain fractional time interval of said longestrepetition period the amount of time that the startof said second fastdeecting wave is advanced with respect to said mid-point of the fulldeflecting wave cycle, causing the pulse corresponding to saidlast-counted timing mark and at least one group of pulses having ashorter repetition period than said longer repetition period to appearas timing marks on the fast-sweep trace produced by said secondfast-sweep deflecting wave, causing a timing pulse from one` of saidgroups having one of the shorter repetition periods to appear as acrosshair mark on the rst part of the trace produced

